Not applicable.
This invention relates to radio frequency (RF) antennas and more particularly to an RF phased array antenna.
As is known in the art, satellite communication systems include a satellite which includes a satellite transmitter and a satellite receiver through which the satellite transmits signals to and receives signals from other communication platforms. The communication platforms in communication with the satellite are often located on the surface of the earth or, in the case of airborne platforms, some distance above the surface of the earth. Communication platforms with which satellites communicate can be provided, for example, as so-called ground terminals, airborne stations (e.g. airplane or helicopter terminals) or movable ground based stations (sometimes referred to as mobile communication systems). All of these platforms will be referred to herein as ground-based platforms.
To enable the transmission of radio frequency (RF) signals between the satellite and the ground-based platforms, the ground-based platforms utilize a receive antenna which receives signals from the satellite, for example, and couples the received signals to a receiver circuit in the ground-based platform. The ground-based platforms can also include a transmitter coupled to a transmit antenna. The transmitter generates RF signals which are fed to the transmit antenna and subsequently emitted toward the satellite communication system. The transmit and receive antennas used in the ground-based platforms must thus be capable of providing a communication path between the transmitter and receiver of the ground-based platform and the transmitter and receiver of the satellite.
To establish communication between one or more satellites and the ground-based platform, the antenna on the ground-based platform must be capable of scanning an antenna beam to first locate and then follow the satellite. One approach to scanning an antenna beam is to mechanically steer the antenna mount. This can be accomplished, for example, by mounting an antenna on a gimbal. Some prior art ground-based platforms, for example, utilize gimbal mounted reflector antennas.
Gimbal mounted reflector antennas are relatively simple and low cost antennas. One problem with such antennas, however, is that gimbal-mounted reflector-type antennas are relatively large and bulky and thus do not have an attractive appearance. In addition, such relatively large structures with moving parts can be relatively difficult to mount on platforms such as automobiles and residential homes. Moreover, such antennas can have problems due to animals (e.g. birds) landing on and the antenna and causing it to move. Furthermore, since gimbal-mounted antennas are not typically low profile antennas, objects (e.g. trees) can hit the antenna and breaking the antenna or the gimbal. Moreover, gimbal mechanisms require maintenance which can be costly and time-consuming.
Another type of antenna capable of scanning the antenna beam is an electronically steerable phased array (ESA) antenna. ESA antennas can be low profile and made to have a relatively attractive appearance. One problem with ESA antennas, however, is that they are relatively expensive. Thus, ESA antennas are not typically appropriate for use with low cost ground-based platforms.
It would, therefore, be desirable to provide a reliable antenna having a relatively low profile and which is relatively compact compared with the size of a gimbal mounted reflector antenna and which is relatively low cost compared with relatively expensive conventional ESA antenna.
In accordance with the present invention, an antenna includes a radiator layer having first and second opposing surfaces and a plurality of radiators disposed on a first surface of the radiator layer. Additionally the antenna includes a microelectromechanical systems (MEMS) layer with a plurality of MEMS phase shifters disposed adjacent to the second surface of the radiator layer, each one of the plurality of MEMS phase shifters electromagnetically coupled to at least one of the plurality of radiators. Finally, a beamformer layer is electromagnetically coupled to the MEMS layer, and a spacer layer is disposed between the MEMS layer and the beamformer layer.
With such an arrangement, an antenna is an electronically steerable phased array which is relatively compact, planar and has a relatively low profile and no moving parts. Because of the relatively low loss connections between the layers of the antenna and the reduced losses in the MEMS phase shifters, such an antenna requires no amplifiers between the beamformer layer and the radiator layer, providing a passive phased array having relatively low internal losses. The passive phased array reduces the complexity of the antenna and costs associated with fully populated active phased array antennas. No motors are needed to operate the antenna, so there is no motor noise, or single point failure modes associated with motor controlled devices. The antenna""s low loss characteristics provide a better noise figure (NF) and gain characteristic than prior art antennas. The antenna""s gain performance is equivalent to prior art antennas having a larger aperture.
A second embodiment is provided from antenna having a subarray driver and a plurality of subarrays. Each such subarray includes a plurality of output ports, a plurality of input ports, a microelectromechanical systems (MEMS) layer having a plurality of MEMS phase shifters, and each of the plurality of MEMS phase shifters coupled to a respective one of the subarray outputs. Additionally, each subarray has a plurality of radiators disposed on a radiator layer, and each of the plurality of radiators coupled to a respective one of the plurality of MEMS phase shifters.
With such an arrangement of multiple layers and plurality of subarray structures the entire antenna array aperture can be formed with a rectangular shape having an arbitrary size. Because of the relatively low loss connections between the layers of the subarrays and the reduced losses in the MEMS phase shifters, such an antenna requires no amplifiers in the subarrays, providing a passive phased array having relatively low internal losses.
In accordance with another aspect of the present invention, the antenna includes a subarray driver having a plurality of transmit circuits and a plurality of receive circuits, a plurality of subarrays. The subarrays have a diplexer with a transmit port and a receive port, the transmit port coupled to the respective transmit circuit and the receive port coupled to the respective receive circuit; a subarray beamforming layer having a plurality of output ports. Additionally, the subarrays have a plurality of diplexers having a first port coupled to a respective one of the subarray output ports, a second port and a third port. Finally, the subarray has a microelectromechanical systems (MEMS) layer with a plurality of pairs of MEMS phase shifters, each of a first one of the pair coupled to a respective one of the second port, and each of a first one of the pair coupled to a respective one of the third port, and a plurality of radiators disposed on a radiator layer, each of the plurality of radiators coupled to a respective pair.
With such an arrangement, the antenna is able to operate in a full duplex mode whereby the antenna can simultaneously transmit and receive through a single aperture. Additionally the antenna is capable of independently directing the transmit and receive beams to one of multiple satellites within its scan volume. The antenna has dual simultaneous polarization (i.e. the polarizations for the receive and transmit sub-bands are opposite sense circular and simultaneous). The antenna is fixed during operation and can point transmit and receive beams independently within the scan volume.
In each of the above embodiments, the antenna is provided from manufacturing and assembly techniques that result in the antenna having relatively low losses. Furthermore, the MEMS phase shifters are provided as relatively low loss devices. The combination of the low antenna losses and the low loss phase shifters allows a transmit path of the antenna to use fewer transmit amplifiers compared with the number of amplifiers required in a transmit path of a conventional phased array antenna. Likewise, the combination of the low antenna losses and the low loss phase shifters allows a receive path of the antenna to use fewer receive amplifiers compared with the number of amplifiers required in a receive path of a conventional phased array antenna. Since the antenna includes fewer transmit and receive amplifiers, the antenna can be assembled using relatively simply assembly techniques and the antenna is provided as a relatively low cost phased array antenna.